We have hiked up to Rob Roy Glacier in high summer under a sun-bleached sky, wearing only shorts and T-shirts - grateful for the dappled shade of the beech forest canopy. We've trudged up the track in full winter tramping gear as fat snowflakes drift down from a low, slate-grey ceiling - hungry for glimpses of the glacier through wisps of mist and snow flurries. We have even attempted the trek in the rain, when tendril waterfalls join forces to become angry, swollen cataracts ... such is the allure of the glacier.

But our favourite time is when the valley is dressed in silver crystals after a June hoar frost and our boots crunch through stiff white tussock and over concrete moss. The river is ice-green foam and the spray freezes on our eyelashes and brows and transforms bearded men into Santa Clauses. Where the meagre early winter sunshine penetrates the steep-sided gorge, the air sparkles with dazzling diamond filaments and our breath becomes a visible thing, hanging in little puffy clouds like cartoon speech bubbles.

When our girls and their holiday cousins were little, they believed they were in an enchanted land, and it was easy to keep them skipping and dancing up the steep track, eager to discover what magic lay around the next corner. They half expected to see Aslan and the White Witch.

Icicle swords droop from overhanging rocks as if guarding fairy grottos below and small waterfalls and ponds are frozen in time. Common-place spider webs and ferns become works of art in silver filigree, demanding that we stop and stare in wonder. But we dare not linger for more than a few minutes for fear of freezing solid like the landscape - or victims of the White Witch.

By early afternoon, the sun is brilliant against a sharp blue sky but there is no warmth where it touches and nothing thaws.

You hear the rushing waters of the Rob Roy stream far below in a deep ravine long before you see the glacier-fed cascade. I listen intently, trying to put the sound into words. It's the noisy hiss of static as you try to tune your radio, but with an underlying conversational gurgle, burble or chortle - and then a deafening booming roar as the gorge narrows and the water fights to be first through the gap in the rocks.

As we climb higher, the glacier is visible in snatches through the forest canopy and flimsy waterfalls tumble in tiers from the mountain ridges. It becomes a game to trace and time a mass of spray from where it topples over the frozen ledge to the rocks far below. It is impossible to take in the full height of the mountains towering above unless you lie on your back on the ground.

The last part of the track takes us over and around truck-sized boulders carelessly discarded by the glacier as it retreated up the mountain side to its present-day precarious home, clinging to a rock face below Rob Roy Peak.

We are spellbound again as if it were our first not seventh or eighth trek to the lookout. Under a heavy mantle of snow, the cold blue gleam of the glacier face is blindingly bright - and mesmerisingly beautiful.

In the spring or summer thaw we are stunned as huge slabs of ice on the terminal face lose the fight against gravity and warming temperatures and thunder down the valley in a white cloud - a fearful sight and awful sound, even from a safe vantage point.

With our Leki hiking sticks, sturdy tramping boots, all-weather Goretex jackets and layers of fine merino and possum, high energy snacks, emergency survival gear and 4WD vehicle waiting at the carpark, we modern hikers are as safe and warm and well-prepared as we can be. We reflect back on an expedition made over 100 years ago by English explorer Maud Moreland who ventured up the Matukituki Valley in a horse-drawn dray and climbed up to the glacier in a long skirt and heavy leather boots - long before the swing bridge was built over the river and a well-formed track cut around the cliff faces, slips and boulders.

In 1908, she wrote: "We were now at the entrance of a gorge that looked as if the mountains had been cleft by some terrific force: on one side they rose black and precipitous with trees clinging wherever they could find a little soil but generally they were sheer walls of rock. On our side the mountains were clothed to within a few hundred feet of the top with dense bush.

Leaving the horses tied below we began a toilsome ascent through a belt of tutu - a stout herb growing as high as our shoulders. This bit was very steep, followed by a belt of fern, then across screeds of slate, shale and faces of bare rock with only cracks for footholds when we clung by our fingertips.

The heat grew greater every moment and the glare from the rocks scorched us and made us terribly thirsty as we worked our way from gully to gully.

After a tedious climb we at last saw the head of the gorge - a wonderful sight on which not many eyes have gazed. It is closed by a semi circle of cliffs, precipitous and black. And wedged as it were between three mountain peaks lies an enormous glacier. Not a long river of ice, but a mighty mass of ice, breaking off sharp at the top of the stupendous peaks."

Maud gazed at the glacier one summer day over a century ago, as transfixed by the sight as we are today, searching for words to express the exquisite beauty and power of the vision before her. Our efforts seem trivial next to hers.

Knees turn to jelly on the long trek back down to the car, the steep descent made even more treacherous as we walk forwards but look backwards for fear of missing a view we have not seen on the way up. The swing bridge over the Matukituki River seems higher and longer than earlier in the day as I contrive without success to cross it alone without the added excitement of friends (male) providing an extra thrill by making it even swingier.

Back at the carpark, the temperature is minus 3 and as we drive back to Wanaka in a cosy car, the fast retreating sun stains the snowy mountain tops pink. We stop at a tiny pebbled beach near Glendu Bay and watch the shimmering pathway shrink to a sliver and disappear as the winter sun puts on a final dazzling display of crimson fire before sliding behind Mt Aspiring/Tititea.

There is silence as we store the memories in a safe place - until next time.

The glacier sits below the 2606m Rob Roy Peak named in early times after Scottish hero Rob Roy McGregor. It is said the figure of McGregor showed on the rock and ice face of the mountain when seen from the Rob Roy Downs opposite the mouth of the stream.

The 50-60 minute, 54km drive from Wanaka to the start of the Rob Roy track is a highlight in its own right. The road skirts Lake Wanaka, passing by iconic Glendu Bay with postcard views of Mt Aspiring and the wispy waterfalls of Treble Cone. It follows the gin-clear Matukituki River up the valley, deep into the Mt Aspiring National Park, part of Te Wahipounamu UNESCO World Heritage site, known to the original Maori inhabitants as Te Wai Pounamu - the greenstone waters.

You can drive to the Raspberry Creek car park and hike to Rob Roy glacier independently or contact Eco Wanaka Adventures for a great guided trek, including lunch and transport from Wanaka.